Estradiol (E), acting at its receptors (ERa and ERp) exert powerful effects on neural functions. A growing literature clearly demonstrates that the actions of estradiol are tissue-specific and developmentally dependent, creating the possibility for unwanted and potentially dangerous side effects of estrogen treatment. Alarmingly, estradiol is widely used clinically despite a full understanding of its actions, which has lead to behavioral and mood disorders in women using oral contraceptives. Furthermore, estradiol has recently been associated with a number of neurological disorders including Parkinson's, Alzheimer's, and stroke. Therefore, it is essential to uncover the mechanisms by which E and ERs exert their specific actions within the brain. Using the mammalian brain as a novel in vivo model for ERa and ERP interactions, this proposal will investigate the underlying mechanisms of ERp's newly discovered inhibitory functions of ERa. The first experiment will utilize selective ERa and ERp agonists, along with immunocytochemistry to explore the role of transiently expressed ERp over ERa during development. The second experiment will use dual label immunofluorescence, confocal microscopy, and co-immunoprecipitations to explore the mechanisms behind ER3's inhibitory role over ERa. The third set of experiments will test the hypothesis that ERa activity will be enhanced by the reduction of ER(3 expression using small interfering RNA. This proposal will address the mechanisms behind ERa and ERp interactions that take place in the developing brain. This proposal will elucidate the mechanism by which estradiol exerts it's effects through interactions with ERa and ERp in the developing mammalian brain. This research will contribute to the poorly understood actions of estradiol in the brain which will support the advancement of reducing potentially harmful neural and behavioral side effects of hormonal drug treatments in women.